Electrophysiology catheters have been in common use in medical practice for many years. They are used to map and stimulate electrical activity in the heart and to ablate sites of aberrant electrical activity. Among the various types of electrodes used in constructing electrophysiology catheters are ring electrodes. These are metal rings positioned at various intervals along the length of the tip section. The ring electrodes are electrically connected, via electrode lead wires which extend through a lumen in the catheter, to electrical instruments, e.g., a monitor, stimulator or source of energy, e.g., RF energy, for ablation.
A conventional method for making the electrical connection between an electrode lead wire and a ring electrode is to draw the electric lead wire out of a lumen in the tip section through an exit hole that extends from the lumen to the side surface of the shaft of the catheter tip. The distal end of the electrode lead wire, stripped of any non-conductive coating, is then welded or soldered onto the inner surface of a ring electrode. The ring electrode is then slipped over the tip shaft to a position directly over the exit hole while drawing the electrode lead wire back into the lumen. The ring electrode is then secured in place, e.g., by swaging or by the application of an appropriate adhesive. A resin, e.g., polyurethane resin, is often applied to the margins or edges of the ring electrode to assure a smooth transition between the outer circumferential surface of the ring electrode and the outer circumferential surface of the catheter shaft.
Conventional methods for mounting ring electrodes on a catheter have certain drawbacks. For example, because the electrode lead wire must be drawn back into the lumen of the catheter tip section as the ring is slipped over the shaft of the tip section, the exit hole cannot be sealed and visually inspected before the ring electrode is swaged or glued over the exit hole. Further, the ring electrode must have a sufficiently larger diameter than that of the shaft of the catheter tip to slide over the shaft to its final position. Stretching the shaft of the tip section to reduce its diameter is one technique that allows the use of a closer fitting ring electrode. This technique, however, is operator dependent and tends to lead to inconsistent quality in the placement of the ring electrode on the shaft. Further, ring electrodes mounted by the conventional method tend to “pull away” from the shaft of the tip section, i.e., the edge of the ring electrode tends to separate from the surface of the catheter tip shaft along the outside of the curve, during tight bending of the tip section.
Other methods include laser welding, for example, laser melting through a ring electrode to create a laser-welded low ohmic electrical connection to a lead wire. Laser welding however relies on accurate location of the lead wire under the ring electrode during welding. Like conventional resistance welding of ring electrodes, laser welding is manual labor intensive and time-consuming operation that is prone to electrical defects due to improper workmanship methods. Moreover, since catheter tubing is pierced with holes to pass the lead wire from a lumen to outside the tubing, the holes must be made fluid tight after ring placement over the tubing.
Another method is disclosed in US Publication 2005/0097737 A1. Therein, a ring electrode with a flared skirt is swaged to reduce its inner and outer diameter so that it is tightly secured to a tip shaft and makes sufficient pressure contact with underlying electrode lead wire to provide a low ohmic connection. Although the process eliminates ring resistance welding, the low ohmic connections may not be stable long term due to the tendency for stress relaxation of the tubing elastomeric material.
For these and other reasons, there is a need to find a method for attaching ring electrodes to the shaft of the catheter tip section that is less costly, more efficient and does not exhibit the above mentioned drawbacks and disadvantages of the conventional method.